1. Field of the Invention
The invention relates to a method for controlling and/or maintaining the temperature of a melt, preferably a steel melt, wherein the temperature of the melt is measured in a vessel, the measured result is compared with a preset temperature range in the form of SPECIFIED values, and so much heat is supplied to the melt by electrical induction by means of an induction coil or removed from the melt by means of a cooling device that the temperature is within the SPECIFIED range. The invention also concerns a device for performing the method.
2. Description of the Related Art
During continuous casting, in particular of steel, a temperature of the melt as uniform as possible, respectively, maintaining a narrow temperature window is desirable in the distribution vessel, in the following also referred to as tundish, for quality and operational reasons. As a result of temperature losses of the melt within the ladle, during transfer from the ladle into the distributor and in the distributor itself, the casting duration is temporally limited.
By mounting a device for temperature control of the melt within the distribution vessel, different melt temperatures within the ladle can be compensated within the distributor and the possible casting duration can be extended. The advantages of such device furthermore reside in a greater flexibility when casting disturbances occur and, primarily, in the more uniform temperature level within the tundish. Quality advantages of the continuous casting product are expected from these measures. Also, casting closer to the liquids is possible.
Known devices for controlling the temperature in the distributor are, for example, plasma heating devices which are conventionally positioned above the distributor. The principle of plasma heating resides in that in a chamber, following vertically the filling level within the tundish, an electric arc is transmitted by electrodes onto a free metal surface. The arc is stabilized by argon; therefore the term plasma. In the area of the chamber a hot spot results and the steel must be guided past it, either across dams or banks or additional flushing devices, for example, porous bottom flushing devices that are permeable for gas.
A disadvantage of this method variant is the required free surface area of the melt within the chamber so that physical and chemical ad interactions between the chamber atmosphere and the melt are to be expected. As a result of the very high temperatures within the electric arc, steam and dust development will occur within the chamber.
Moreover, inductive tundish heating devices are known in which a differentiation is made between the so-called crucible inductors and gutter or channel inductors which are usually connected by being fixedly flanged with the construction components of the distributor. In this connection, the gutter inductors, relative to the crucible inductors, are comparatively complex in regard to manufacture and maintenance.
U.S. Pat. No. 5,084,089 describes induction coils arranged stationarily externally in a depressed area of a distributor and a cooling device immersed into the melt within the distributor for controlling the melt temperature.
Advantages of inductive heating result because of the lack of contact with the melt as well as the force generation within the melt stemming from the induced electromagnetic alternating field which causes a stirring movement of the melt and thus a faster heat distribution within the distribution vessel. Disadvantages of the above listed inductive tundish heating devices result from the fixed attachment to the tundish, which has a negative effect with regard to flexibility. Also, the required service and maintenance expenditures are significant.
The patent application DE 197 52 548 A1, not yet published at the time of filing of this application, concerns a method for controlling and maintaining the temperature, in particular of a steel melt, within narrow temperature limits over the casting duration of continuous casting wherein lowering of the temperature is compensated by heating. This method is improved in that the temperature of the melt is measured at the outlet of the distribution vessel, the measured result is compared with the preset lower temperature limit, and the melt, when reaching or falling below the limit, is heated until the temperature [makes possible an] advantageous temperature control of a metal melt in a distribution vessel.
For solving this object, it is suggested with the invention that in a method of the kind mentioned in the preamble of claim 1 for controlling the melt temperature an induction coil received in a refractory shaped part closed off at the bottom is immersed into the melt. The heating output of the device, in the following also referred to as a heating rod, is controlled by the current intensity of the current flowing through the induction coil. The induction coil is cooled from the interior and/or exterior by a cooling fluid, preferably air.
In this connection, the method suggests that heat is transmitted to the melt by thermal conduction via the wall of the shaped part which, in turn, is coupled to the induced electromagnetic alternating field.
As an alternative, heat can be supplied to the melt by means of coupling of the electromagnetic alternating field. Also, it is possible to remove heat from the melt by means of thermal conduction through the wall of the shaped part.
The invention comprises moreover a device for performing the method according to the invention, wherein the shaped part is provided with a refractory tube, that is closed at the bottom and can be inductively coupled and that receives the induction coil in an
Based on the aforementioned prior art, it is an object of the invention to provide a method of the aforementioned kind as well as a device suitable for performing the method which, while avoiding the disadvantages and difficulties present in the prior art, provide a technically uncomplicated, flexible and thus economically advantageous temperature control of a metal melt in a distribution vessel.